1. Field of the invention
The present invention relates to a surge protecting device for protecting circuits or electric power units of electronic devices from surges.
2. Description of the Related Art
Generally, electronic products, such as a television set or a VCR, have an antenna. It is possible for external surges caused by lightning, for example to cause a current surge into the electronic device. The surges flowing into an electric power unit or internal electronic parts of the electronic devices may cause damage or break-down in the devices.
Accordingly, it is advantageous to provide a proper measure to comply with safety rules to protect electronic devices against surges flowing into the devices.
Referring to FIG. 1, a prior art schematic circuit diagram illustrates the construction of an electronic product having a protective device for protecting against surges.
As shown in FIG. 1, a surge protecting device 10 is formed on a printed circuit board 20 with a T-shaped gap 11 having a crevice of a predetermined distance t therein, and device 10 is provided with a surge inflow terminal 12 and surge absorption terminals 104 and 116 made of a plurality of copper pieces sized to fit in the gap 11. The device 10 is patterned on printed circuit board 20.
The surge inflow terminal 12 is typically disposed at the center of the device 10 to be connected to an antenna 50, and the surge absorption terminals 104 and 116 are arranged such that gap 11 separates terminals 104 and 116 from each other and from the surge inflow terminal 12. Terminals 104 and 116 connect to alternating current (A.C.) wires 30 and 40, respectively.
When the surges caused by an event, for example, a lightning strike flow into the surge inflow terminal 12 through the antenna 50, a spark is generated in the gap 11 between the surge absorption terminals 104 and 116. An arc discharge generated in the gap 11 results in converting part of the surge energy into heat to be dissipated in air, and the rest of the energy is dissipated in a ground through an A.C. electric power line 40.
Even though overvoltage is generated between terminals of the A.C. electric power lines 30 and 40, the surge absorption terminals 104 and 116, connected with the lines 30 and 40, are normally designed to be insulated therebetween. When an arc caused by the overvoltage is generated, the energy of the overvoltage is dissipated through the power line 40, thereby protecting internal circuit elements of the electronic devices from damage.
However, there is a problem in the prior art surge protection device 10. Though it is low in cost, when it is made of a copper foil on the printed circuit board 20, flux left by soldering frequently remains on the printed circuit board 20 thereby making it difficult to create a spark discharge in the gap between the surge absorption terminals 104 and 116.
When the surges are continuously received in the surge inflow terminal 12 through the antenna 50, the copper foils on the printed circuit board 10 may burn, and a spark discharge cannot be generated, or the device fails to perform as a surge absorption device.
When the surge protector is damaged, it is inconvenient for a user to repair it because the entire printed circuit board 20 must be replaced, thereby increasing cost. Therefore, a need exists for a surge protection device for electronic devices, in which the surge protection device can withstand a multiplicitity of surges.
A conventional device 10 for protecting electronic parts against surges was tested. One model of a prior art device is model LSS-15SC manufactured by Noise Company. This model was tested by repeatedly applying negative voltage to an antenna terminal instead of an exterior surge from lightning. The results of the test are as follows in Table 1:
TABLE 1 ______________________________________ The number of times voltage Result of Voltage(KV) was applied Failure Part damaged Note ______________________________________ 5 1(first) no power IC803 (for standby) 6 1(first) no power IC803 7 2(second) no power IC803, D802 8 2(second) no power IC803 9 1(first) no power IC803 10 1(first) power-off none normal at the start of power-on 2(second) no power F802(fuse), IC803 11 1(first) no power F802 12 filter of the inside line of an A.C. electric cord burnt 13 1(first) no power F802 ______________________________________
From the results of the test, it was found that circuit devices are not well protected from surges and easily broken down at the first stage of the test.